With respect to this type of conventional tires, for example, JP2000-225810A (or corresponding U.S. Pat. No. 6,578,611B2) discloses a tire including a main belt wherein two plies of narrow belt layers on the inner layer side and two plies of wide belt layers on an outer layer side, which are wider than the narrow belt layers, are sequentially arranged on the outer periphery of the crown region in a radial carcass to extend along the crown region within a widthwise sectional plane of the tire. In such conventional tires, the belt cords of the narrow belt layers extend in such a direction as to intersect the tire equatorial plane with a relatively small angle. Thus, these narrow belt layers serve to bear the circumferential tension to suppress diametrical growth of the tire, thereby preventing change in the crown shape during rolling of the tire under a loaded condition. Moreover, the provision of relatively narrow belt layers serves to mitigate the strain occurring at the side edges of the belt layers.
On the other hand, as for the wide belt layers, the intersection angle of the belt cords relative to the tire equatorial plane is made larger than that of the belt cords of the narrow belt layers and the belt width is made larger than the width of the narrow belt layers so as to provide an enhanced intra-plane rigidity of the belt, thereby providing excellent kinetic performance, such as turning property of the tire during cornering of the vehicle, straight running stability, etc.
In this instance, for example, it is considered necessary for the belt cords of the two narrow belt layers on the inner layer side to extend in mutually opposite directions relative to the tire equatorial plane so as to intersect each other, in order that the belt tension is borne by the belt cords. Also, it is considered necessary for the belt cords of the two wide belt layers on the outer layer side to similarly intersect each other between the layers, in order that the belt exhibits a high intra-plane rigidity.
Moreover, it is known that if the belt cords of the second layer forming the narrow belt layer and the third layer formed by the wide belt layer, both as counted from the radially inner side, extend in mutually opposite directions relative to the tire equatorial plane so as to intersect each other between the layers, then the belt cords of the innermost narrow belt layer and the wide belt layer as the third layer extend in the same direction, so as to suppress the relative shearing strain between the side edges of the innermost narrow belt layer and the third layer forming the wide belt layer, which are adjacent to each other in the radial direction, thereby preventing concentration of strain at the side edges of the innermost narrow belt layer.
Therefore, with respect to the main belt, it is considered preferable for the belt cords of all the layers to extend with intersection to each other between the adjacent layers, so as to suppress the diametrical growth of the tire and provide high intra-plane and extra-plane rigidities of the belt, thereby dispersing the strain occurring at the side edges of the belt layers.
However, with the conventional tires as explained above, when it is intended to suppress the diametrical growth of the tire by arranging the belt cords of the two narrow belt layers on the inner layer side, since the belt cords of the second narrow belt layer and the third layer formed by the wide belt layer, as seen from the radially inner side, are arranged to intersect each other, it is difficult to sufficiently suppress formation of cracks from the side edges of the two narrow belt layers on the inner layer side, to achieve an intended suppression of the diametrical growth of the tire, and to provide high intra-plane and extra-plane rigidities of the belt.
To cope with such a problem, there has been proposed to suppress formation of cracks from the side edges of the belt layers by applying a coating rubber to the side edges of the belt layers, or selecting the modulus of elasticity of the interlayer rubber for the neighboring portions of the side edges of the belt layers. However, these proposals are still incapable of sufficiently suppressing growth of cracks from the side edges of the belt layers.